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Author Topic: 87 k10 350 tbi tuning?  (Read 12232 times)

Offline VileZambonie

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Re: 87 k10 350 tbi tuning?
« Reply #30 on: March 16, 2023, 02:31:24 PM »
The ECM grounds the solenoid to energize it and allow vacuum to the EGR valve.
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Offline JohnnyPopper

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Re: 87 k10 350 tbi tuning?
« Reply #31 on: March 16, 2023, 05:51:27 PM »
Ahh, so normally closed. Thx man!

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1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline JohnnyPopper

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Re: 87 k10 350 tbi tuning?
« Reply #32 on: March 20, 2023, 11:34:14 AM »
Well the last salvo from the parts cannon did not do the trick. New EGR and Control Module.

Same symptoms, won't idle, have to feather the throttle to keep rpm's up, to a point she back fires slightly.

Trying to keep her on long enough to have some codes thrown, none yet.
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1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline VileZambonie

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Re: 87 k10 350 tbi tuning?
« Reply #33 on: March 20, 2023, 06:04:55 PM »
It sounded to me like you said eliminating the EGR cured the issue. Not sure what you replaced but if you again unhook the EGR and the problem goes away, there is still an issue there.
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Offline JohnnyPopper

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Re: 87 k10 350 tbi tuning?
« Reply #34 on: March 20, 2023, 06:45:01 PM »
Well disconnecting the EGR made a difference in how it ran, in that I could advance the rpm higher.

It was leaking, so replacement was in order.

I could pass air through the module while disconnected, so that suggested a leak when not energized.

Still waiting for some code.

Since the replacement should I power cycle the ECM?
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1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline VileZambonie

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Re: 87 k10 350 tbi tuning?
« Reply #35 on: March 21, 2023, 04:26:21 PM »
Have you confirmed there is no suction at the hose at the EGR valve with the engine running now?
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74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline JohnnyPopper

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Re: 87 k10 350 tbi tuning?
« Reply #36 on: March 21, 2023, 06:37:31 PM »
Yes I did what you suggested earlier, I disco'd the hose off the EGR valve.
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1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline VileZambonie

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Re: 87 k10 350 tbi tuning?
« Reply #37 on: March 21, 2023, 06:55:48 PM »
and there is no vacuum present now after you've replaced the solenoid right?
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74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline JohnnyPopper

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Re: 87 k10 350 tbi tuning?
« Reply #38 on: March 22, 2023, 01:37:24 PM »
I am unable to ascertain the answer to that VZ, as I have to feather the throttle to keep it running. I can get an assistant to get me to that point, will keep you in the loop. Thx!
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1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline VileZambonie

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Re: 87 k10 350 tbi tuning?
« Reply #39 on: March 22, 2023, 05:42:44 PM »
Do you have an OBDI scan tool?
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74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline JohnnyPopper

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Re: 87 k10 350 tbi tuning?
« Reply #40 on: March 23, 2023, 09:19:12 PM »
No I  use the paperclip method.

Funny thing is it hasn't thrown any code this time, the CE light comes on during starting.

I am hoping that feathering the throttle over several times it will stay on.
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1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline VileZambonie

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Re: 87 k10 350 tbi tuning?
« Reply #41 on: March 25, 2023, 08:03:22 AM »
We need to see your data, codes are great for doing specific tests but live data shows us what the ecm is seeing. You should get one, there's plenty of cheap options.

If you confirm there is no vacuum present at the EGR and it is not hanging it open, next check for vacuum leaks including the base gasket at the TBI. If okay check fuel pressure.
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74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline JohnnyPopper

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Re: 87 k10 350 tbi tuning?
« Reply #42 on: March 27, 2023, 06:56:19 PM »
Well since the 'atmospheric rivers' have subsided and we're not being washed away, I finally hooked up a pressure gauge and NOTHING.

It's not the best gauge according to bd, 0-100 at 10 lb increments, but no reading at all.

It has a bypass valve, that I pressed while feathering the throttle, and gas cycled through.

Just have a nagging doubt about testing the pump before the tank switch prior to going all in with a new pump. Any thoughts?

TIA!
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1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Online bd

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Re: 87 k10 350 tbi tuning?
« Reply #43 on: March 27, 2023, 07:32:49 PM »
Low fuel pressure certainly could cause the symptoms.  So could a plugged filter, but if you actually had "zero" fuel pressure, the engine wouldn't start.  When you say "it has a bypass valve," do you mean a pressure relief valve?  Does the TBI adapter fitting for the gauge tap contain a Schrader or similar check valve, or is it completely open and unrestricted to fuel flow out to the gauge? 

For a grassroots validation of the gauge, if you have an air compressor with a regulator valve, set the regulator to 25 PSI then feed pressure directly into the gauge and compare the readings.

Buy, rent, or borrow a proper test gauge with a suitable fuel tap fitting.  TBI systems demand proper fuel pressure and adequate flow!
« Last Edit: March 28, 2023, 09:06:29 AM by bd »
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Offline JohnnyPopper

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Re: 87 k10 350 tbi tuning?
« Reply #44 on: March 27, 2023, 08:11:58 PM »
The bypass is really a pressure relief valve, connected right below the gauge, with a clear tube to see if there is flow.

Regarding the check valve, it appear as a T fitting that the gauge snaps onto like a spring loaded air tool quick connection.

The adapter hose appears to be straight thru to the TBI. I installed it post inline filter.

Yes, I tested it against my air compressor, 10 psi differential at 80 to 90. That alone could count for no reading, yes?

It runs but not by itself, I have to feather the throttle so it must have some pressure.

The inline filter is new, but the internal screen/filter is not.

Is the pressure regulator monitored by the ECM? Could it be stuck open? 

I could just connect the gauge to the fuel line post filter and read the pump only.
« Last Edit: March 27, 2023, 08:13:46 PM by JohnnyPopper »
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1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction
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